Liz Birt, a parent in Wilmette, Ill., says her son Matthew, 9, gradually developed autism symptoms after receiving two vaccinations when he was 15 months old. (AP Photo/Aynsley Floyd)

The number of children diagnosed with the baffling brain disorder has skyrocketed, with some states seeing sixfold increases in recent years. Many parents blame vaccines for the explosion in autism, which causes bizarre repetitive behavior and an inability to establish emotional ties. Responding to parents' lawsuits against vaccine makers, Congress is attempting to craft legislation that protects drug companies while compensating families. But some experts say better diagnosis could explain autism's apparent rise. Researchers are still teasing out the role of genetics and the environment in their search for autism's cause. Meanwhile, school districts across the country face the daunting prospect of providing federally mandated special instruction — at a yearly cost of up to $60,000 per pupil — to growing numbers of children.